There is already known from U.S. Pat. No. 4,378,601 an optically pumped laser having a securing arrangement for a SLAB type bar. This laser essentially comprises a housing intended to accommodate the bar and in which circulates a cooling fluid. Further, the laser comprises a luminous source arranged on either side of the bar in order to bring about optical pumping in the active medium. The bar is mounted in a securing arrangement which may be introduced into the housing or withdrawn therefrom.
Such securing arrangement comprises on one hand first longitudinal support means having a U-formed section and which are provided with lugs at their ends, these means enveloping the upper and lower faces of the bar, and on the other hand second support means having a complementary configuration to those of the ends of the bar in order to be attachable thereto. The lugs of the first support means cooperate with slots provided in the second support means in order to maintain the bar in a rigid framework intended to be installed in a housing.
This securing means has the advantage of being capable of rigidly maintaining the bar in the laser without causing mechanical stresses in the latter. One thus avoids risks of variations in the refractive index in the bar, such variations having as an effect to change the quality of the laser beam.
However, this arrangement also gives rise to a difficulty. Effectively, since the bar is totally immersed in the cooling fluid except for its extremities, the lateral faces thereof are cooled just as the upper and lower faces. Consequently, the temperature profile following a path perpendicular to the upper and lower faces of the bar, varies according to whether the path is close to or remote from a lateral face, and this brings about edge effects diminishing the yield of the laser.
Another arrangement for securing the bar in a laser described in U.S. Pat. No. 4,761,789, attempts to overcome this difficulty in isolating the lateral faces of the bar from the cooling fluid. This laser comprises a bar placed between two transparent laminae, the bar and the laminae being arranged between two supporting plates, each of which includes a rectangular opening which extends substantially over the length of the bar. Sealing gaskets assure the sealing at the periphery of the opening between the laminae and the supporting plates. To these openings are adapted pumping reflectors having a cross-section substantially in the form of a U which, with the laminae, bound a circulation space for a cooling fluid as well as a housing for an optical excitation source for the bar. Finally, between each supporting plate and the outer framework is provided a bracing frame bounding a second cooling channel, the assembly being mechanically clamped in order to guarantee good securing of the bar and good sealing.
At the same time, the solution suggested by the above-mentioned document does not bring about entire satisfaction. Effectively, during the mechanical clamping of the assembly, the clamping effort is not controlled with the result that it is very difficult to obtain an appropriate clamping.
If the clamping force is too great, there result mechanical stresses in the bar and thence variations in the refractive index which change the quality of the beam.
On the other hand, if the clamping force is insufficient, the transmission of the quantity of heat through the laminae, the support plates etc. diminishes thereby causing a drop in the laser yield.
The invention has as its main purpose to remedy the difficulties of the above-mentioned prior art in disclosing a laser provided with a securing arrangement for the bar eliminating the influence of the clamping force while thermally insulating the lateral faces of the bar.